Stock-Based Compensation, Nonvested Restricted Stock Awards (Details) - Restricted Stock Awards [Member]	12 Months Ended
Dec. 31, 2018 $ / shares shares
Number of Shares [Roll Forward]
Nonvested at beginning of year (in shares) \| shares	562,800
Granted (in shares) \| shares	202,700
Vested (in shares) \| shares	(233,900)
Forfeited (in shares) \| shares	(64,000)
Nonvested at end of year (in shares) \| shares	467,600
Weighted-Average Grant Date Fair Value [Abstract]
Nonvested, beginning balance (in dollars per share) \| $ / shares	$ 51.17
Granted (in dollars per share) \| $ / shares	72.62
Vested (in dollars per share) \| $ / shares	56.00
Forfeited (in dollars per share) \| $ / shares	54.40
Nonvested, Ending Balance (in dollars per share) \| $ / shares	$ 57.61

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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-Publisher FASB
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-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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No definition available.

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